Cataract is when the lens inside the eye becomes cloudy, usually with age, but can develop earlier following previous eye surgery, trauma, or if you have diabetes. Depending on how much and the type of cataract, symptoms can include gradually worsening blurry vision, ghosting or glare in sunshine or in the dark. Cataracts usually develop slowly so most of the time people don't notice the slow deterioration in their vision until they have a sight test by an Optician. Everyone develops cataract to some degree as they get older, and in 1 in 3 people it becomes significant enough to require surgery to help restore visual clarity.
Changing your glasses or contact lens prescription may help with early cataract, however these tend to need updating more frequently when the cataract is developing. Eventually as your cataract worsens, stronger glasses no longer improve your sight. The time to have cataract surgery (termed "phacoemulsification and IOL") is when you can longer see clearly enough to do your usual activities or hobbies even with glasses or contact lens on.